Human cartilage has very unique properties. It is one of the few avascular tissues in the body. It serves to prevent bone growth into the articulating surface of joints, which would otherwise interfere with the motion of such joints. Cartilage is semipermeable and receives its nutrients from the synovial fluid which surrounds cartilaginous tissue in articulating joints and which diffuses into the cartilage during motion of the joint. Cartilage itself also possesses viscoelastic and lubricating properties. Materials which are proposed for use in the repair or replacement of natural cartilage must possess physical and mechanical properties which are as close as possible to those of natural cartilage.
Younger persons, ranging in age from children to young adults, often engage extensively in rigorous athletic activities, such as skiing, surfing, football, basketball, and even roller blading, which frequently results in accidents which cause traumatic injury to cartilage, particularly that surrounding the knees, elbows, and shoulders. In the U.S. alone, there are well over 300,000 such injuries per year. Most of these injuries are to the anterior cruciate ligament of the knee, which frequently becomes torn. Younger persons are also occasionally afflicted with arthritic diseases, such as juvenile rheumatoid and osteoarthritis, which cause degeneration of cartilage. Osteoarthritis may also set-in following a traumatic injury to cartilage which is not repaired or is repaired improperly, leading to a further deterioration of the previously damaged cartilage. The extent of the cartilage defect, resulting either from traumatic injury or chronic disease, can vary considerably from a small area to a larger, more widespread area, or even involve all of the cartilage of an entire joint, depending on the extent of the injury or the extent of the spread of the disease. When the defect is caused by traumatic injury and is extensive enough in size to involve a large mass of cartilage, the damage is not capable of self-healing. Heretofore it was not possible to repair extensive cartilage defects. Such damaged cartilage had to be removed and replaced. Often this required complete joint replacement surgery. Cartilage which has become defective through damage caused by traumatic injury from accident, whether sports related or from other causes, such as an automobile accident, as well as cartilage which has become defective as a result of deterioration due to the spread of a chronic degenerative disease, also typically gives rise to and is accompanied by severe pain, especially where the sites of the damage or disease is proximal to or constitutes part of an articulating joint surface, such as the knee. The damaged or diseased portion of the cartilage is usually also accompanied by swelling of the surrounding tissue; and, where an articulating joint is involved, a disruption in the flow of lubricating synovial fluid around the joint often occurs, which, in addition to being a cause of the source of pain, usually leads to further mechanical abrasion, wear, and deterioration of the cartilage itself, finally resulting in the onset of osteoarthritis and complete disablement of the articulating joint, ultimately requiring complete replacement of the joint.
Historically the only choices available to patients with cartilage damage, especially the cartilage of an articulating joint, such as a knee or elbow, were to initially do nothing if the extent of the damage was only relatively minor in scope, which sooner or later usually led to a worsening of the condition and further damage to the cartilage and to the joint itself, with the patient feeling discomfort and pain when using the joint, thus ultimately requiring a complete joint replacement to restore mobility; or, if the extent of the damage was significant to start with, to immediately perform a complete joint replacement. In the case of very young patients, however, complete replacement of a joint is problematic in that the patient's overall skeletal bone structure is not yet fully developed and is still growing, so that the replaced joint may actually be outgrown and no longer be of appropriate size for the patient when their fully matured adult size, stature, and skeletal structure is attained. Moreover, in the past, many replacement knee, elbow joints and shoulder joints have typically had a maximum active useful life of only about ten years, due to wear and tear and erosion of the articulating surfaces of the joint with repetitive use over time, thereby necessitating periodic invasive surgery to replace the entire joint. For a very young patient this meant that they would have to face the prospect for several more such surgeries over their lifetime, notwithstanding progress and improvements in the wearability of materials used for joint surfaces that have been made and continue to be made as new materials are developed.
In recent years a large number of devices and methods for the replacement of defective portions of natural cartilage have been proposed. Some of these have been directed at enabling the repair of larger portions of defective cartilage without having to resort to a full joint replacement, when an articulating joint is involved. Some of the proposed devices are made from natural cartilage which has been self-harvested or harvested from cadaveric sources, some devices are based on composite artificial materials, and some methods involve the growth of new natural cartilage material. A few of the proposed methods for natural cartilage replacement utilize artificial cartilage devices in the form of pre-formed plugs, which are used to fill-in void cavities created by the resection and removal of the damaged or diseased portion of cartilage from the patient.
The various approaches to the problem of cartilage repair and replacement can broadly be divided into those offering a long-term solution, and those offering a short-term solution. Biological approaches involving the growth of new replacement cartilage, either within or without the patient, are generally considered long-term solutions because of the time needed to regenerate the cartilage; while essentially mechanical approaches involving the implant of pre-formed devices or plugs or the in situ formation of cartilage replacement plugs or devices are considered short term solutions because they can usually be effected immediately by surgical procedures which can be completed in a relatively shorter period of time, and which, therefore, are capable of alleviating a patient's accompanying pain and of rehabilitating a patient in a shorter time span. There are, however, several major problems and disadvantages associated with all of the various prior art cartilage replacement devices and methods which have heretofore been proposed.
The use of naturally derived cartilage plugs presents the major problems of lack of availability, limitations on the size of the repair that can be effected, and high potential for infection and transmission of disease. In some instances it has been proposed, for minor cartilage replacement procedures which involve the replacement of relatively small volumes of cartilage, that the cartilage be harvested from the patient by excising a portion of cartilage of suitable size from a donor site on the patient's body. Where the portion of damaged or diseased cartilage that is to be replaced is more extensive, however, such a self-harvesting procedure is not feasible because a sufficiently large plug cannot be extracted from another site without causing damage to or a weakening of the cartilage and underlying bone at the place of harvesting, or when being harvested from a site at or near another articulating joint, without causing damage to the operability of the articulating joint itself at the point of harvesting. Moreover, there are a limited number of suitable locations on the body from which cartilage can be extracted for use elsewhere. Such a self-harvesting procedure actually involves dual surgical procedures of first performing the harvesting procedure at one situs on the patient, followed by the replacement procedure at another situs on the patient. Depending on the age and overall health of the patient, as well as on other considerations, it may not be feasible to perform both procedures at the same time. Moreover, non-medical considerations must be taken into account. Such a dual procedure is time consuming and costly, and may be objected to on cost grounds in some insurance or managed care contexts. Because the procedures are invasive, there is the additional risk of infection and pain to the patient occasioned by the need for two separate surgical procedures, at the cartilage harvesting site and at the cartilage repair emplacement site.
As an alternative to such a self-harvesting procedure, some have proposed that cadaveric cartilage specimens be extracted and used. This alternative, however, also presents the same problems of limited sources of availability and potential for infection or transmission of disease. In cases where it is necessary to reset larger portions of damaged or diseased cartilage from a patient, although procedures utilizing natural cartilage replacement plugs derived from cadaveric sources are not limited by considerations as to the amount of cartilage that can be excised from a particular location in order to preclude damage to or a weakening of the remaining cartilage and/or the joint, at the donor site, as occurs in a self-harvesting situation, there are still limitations as to the total amount of suitable cartilage that can be harvested from cadaveric sources, and the overall reliability of obtaining acceptable cadaveric cartilage sources at all is not high. In addition to the threat of infection to the recipient patient from other external sources, moreover, care must be taken that there is no chance of transmitting any disease carried by the cadaveric donor to the recipient.
One of the long term methods proposed by the prior art involves the regrowth of replacement natural cartilage material in the void cavity formed by the resection of damaged or diseased cartilage. Attempts have been made to isolate and culture chondrocytes or stem cells in vitro. These cells are then implanted or injected into the cartilage defects in order to promote healing. Another such long-term method utilizes morphogenetic growth factors to inductively stimulate cartilage repair. Some of the obstacles to this latter method involve the selection of one or more appropriate growth factors; the selection of appropriate delivery vehicles for controlled, time-release of the growth factors to ensure that the proper concentration of growth factor is maintained at the implant site; and necrosis of immature or newly regenerated tissue under stress or when subjected to loading conditions.
An example of one such long-term method, and the compositions for effecting the method, is disclosed in U.S. Pat. No. 5,723,331 to Tubo et al. for “Methods and Compositions for the Repair of Articular Cartilage Defects in Mammals”. The method involves the use of denuded chondrogenic cells which are proliferated ex vivo as monolayer cultures in order to expand the pool of available chondrogenic cells. The proliferated cells are then seeded in a pre-shaped well having a cell contacting, adhesive surface. These cells redifferentiate and begin to excrete cartilage-specific extracellular matrix.
The principal disadvantages of this method are that it is very complicated and time consuming, requiring up to several months to fully culture the cartilage cells to the point where they are available for use in a preformed shape. This method also faces the obstacles facing all such long-term methods mentioned above.
In the area of short-term, interim solutions, attempts have been made to repair or resurface cartilage defects with implantable medical devices made from biocompatible materials. For example, the use of collagen sponges has been proposed as an implant to promote cartilaginous tissue ingrowth, however, this method has not demonstrated good long-term success. The use of an injectable liquid polyurethane and poly ethyl methacrylate has also been proposed. These systems are based on arthroscopic injection of the reactive liquid composition at the site of the cartilage defect. The composition then sets in situ. From a practical viewpoint, these methods are limited to those applications where the surrounding cartilage forms a natural cartilage capsule that is capable to acting as a mold to contain and shape the injected liquid composition until it sets. According to some proposed methods, the injected material is capable of being arthroscopically shaped after it has been injected. A major disadvantage of using reactive polyurethane-based systems is that residue diisocyanate in the reactant becomes hydrolyzed in the presence of moisture, to diamine, which is both toxic and carcinogenic.
One such method based on the injection of a reactive polyurethane system with arthroscopic shaping of the injected mass is disclosed in U.S. Pat. No. 4,743,632 to Marinovic for “Polyurethane Urea Polymers as Space Filling Tissue Adhesives”. According to this method, polyurethane urea polymers are prepared by mixing purified isocyanate polyurethane prepolymers with an aqueous solution of an amino, ureido, or hydroxyl substituted amine or a like-substituted alpha-amino acid. The composition, while still in liquid form, is injected into a cavity where it solidifies.
Another reactive system is disclosed in U.S. Pat. No. 5,556,429 to Felt for “Joint Resurfacing System”. The system involves a method that includes the delivery of a curable biomaterial, which is a composite of two or more materials, particularly those comprising two phase systems formed from a polymeric matrix and a hydrogel filler. The polymeric materials include polyurethane, polyethylenes, polypropylenes, polyvinyl chlorides, and others. Matrix materials include silicone polymers and polyurethane polymers. The hydrogels are water-containing gels. The composition is introduced in liquid form, by minimally invasive means, such as by arthroscopic injection, followed by in situ curing of the material, such as by exposing the liquid polymer to ultraviolet light, and shaping and contouring of the cured material, which is also performed arthroscopically.
One of the prior art artificial cartilage replacement devices and methods is disclosed in U.S. Pat. No. 5,067,964 to Richmond et al. for “Articular Surface Repair”. The cartilage repair piece disclosed there is a composite which includes a backing layer of non-woven, felted fibrous material, which is conformable to flat and curved surfaces. The front face of the backing layer is either uncoated or covered by a coating of a tough pliable material having a front surface which is tough smooth and slippery in the presence of synovial fluid, so that the device responds naturally at an interface with other cartilage. A disadvantage associated with such approach is inherent in the lack of any physical anchoring to the underlying bone.
A disadvantage and limitation of this method and this type of cartilage replacement device is that it requires cell ingrowth into the felted backing for biologic fixation of the device. This type of soft tissue fixation is less desirable than fixation achieved by bone ingrowth or fixation directly with bone without a fibrous tissue interface. Their device is composed of a layer of polymer attached to a porous felt like backing which may fatigue with motion and result in delamination. Moreover, this type of failure may occur before biologic fixation occurs resulting in failure of the device. In addition, their device is flexible to achieve conformation with the cartilage surface and may not allow adequate weight bearing. In contrast, our device is already structurally adequate to withstand full weight bearing immediately without the need to develop biologic fixation.
Instruments for resecting cartilage, such as for excising a plug of damaged or diseased cartilage, are known in the art. U.S. Pat. No. 4,641,651 to Card for “Cartilage Punch and Modified Prosthesis in Tympanoplasty” discloses a cartilage punch for removing a cartilage plug of uniform thickness. The instruments associated with the present invention are customized for effecting the various steps of the procedure according to the present invention, and include instruments for resecting the damaged or diseased cartilage, for shaping the resulting void, and for implanting the replacement cartilage plug.
Published World Intellectual Property Organization Patent Application WO 96/27333 of Hart et al. to Innovasive Devices, Inc. for “Apparatus and Methods for Articular Cartilage Defect Repair” discloses a bone plug removal tool that includes a cylindrical cutting element having a external surface and an internal surface defining an internal bore extending along a longitudinal axis of the cutting element from a proximal cutting edge.
Accordingly, there is a need in the art of orthopedic replacement surgery, especially for young patients, of a means of replacing resected portions of damaged or diseased cartilage that does not involve extensive invasive surgery or removal of extensive portions of the cartilage beyond the immediately affected portion; in the case of cartilage that constitutes part of an articulating joint such as a knee or elbow, that does not require a full joint replacement when the joint is still substantially viable and motion of the joint has not been completely compromised; which provides for a readily available source for the cartilage material in unlimited quantities; which does not require the harvesting of the material from the recipient or from cadaveric sources; and which offers simplicity and speed both in the production of the cartilage replacement materials itself and in the actual procedure for its implantation.